As for real, well … I didn’t know that you could be three feet away from a building when it blows up and walk away with nothing more than movie-star scratches (cheek, eyebrow). Or that trains roar through the streets of Paris

alongside the cars. Or that a good guy might flip sides because he stumbled on evil technology and thought it was cool.

Duke (Channing Tatum) and Rex (Joseph Gordon-Levitt) are a pair of embryoaged majors (add up their ages and they’d be old enough to be a real major) in a secret military force. Ripcord (Marlon Wayans) is their comedic sidekick.

Duke’s squad hooks up with a secret commando team that calls itself G.I. Joe and is at war with evil counterparts who have no team name but are so inept, I’ll just call them G.I. Schmo.

The toughest Schmo is Duke’s foxy, catsuit-clad ex, Ana (Sienna Miller), who, in a lovers’ snit, decided to dump her guy, dye her blond hair black and also help annihilate the world.

Everyone’s after the ultimate weapon –“nanomites” contained in a suitcase (Samsonite?) that can burst into clouds of what look like bad-ass termites that devour everything in sight in disaster scenes that look like they were recycled from “The Mummy.”

That movie and this one share a director, Stephen Sommers, who also inexplicably places the Joes’ HQ beneath the Great Pyramids (hell, sand worked before), uses the guy who played the Mummy as a baddie named Zartan, and even dusts off

Brendan Fraser, who pops up in the Joes’ training center but has nothing to do but watch G.I. Joe for five minutes.

Which is about how long most viewers are going to be able to stand it. Ana goes to much effort to steal back the nanomite Samsonite for her boss, a Scottish arms dealer, even though he’s the guy who made the thing in the first place. He also keeps forgetting to check whether his baby’s LoJack is on and giving away his position.

The Schmoes try to destroy Paris, where Ana zooms around holding a weapon that looks like a Super Soaker with a lava lamp stuck to the end. Much of the time, Duke is stuck to the roof of her SUV-like guano. His massive laser guns can’t penetrate the car’s armor, so it’s lucky he brought along a really sophisticated weapon… a sword. Which slices through the SUV like it’s cutting into a boiled yam.

The Joes are so obsessed with gadgets — one suit makes them invisible, another super-fast and impervious to attack from everything except film critics — that they forget to tell the rest of Earth what they’re doing. You might think France would be interested to know that there’s a plot to turn Paris into French toast. (After which, we learn in a scene with the US president, played by Jonathan Pryce, that “the French are very upset.”) Soon we’re under the polar ice cap with Duke a captive to the Schmoes.

You’d think they’d keep him in handcuffs or something. Coming to his rescue, the Joes gain entrance to the Schmo control room by sticking another sword in a security panel, have their martial-arts guy (Snake Eyes) face off in long, irrelevant battles with his Schmo foe (Storm Shadow), and do their best to prevent the Schmoes from destroying the world — although the scheme turns out to be an irrelevant distraction and the movie ends with nothing resolved.

This is the kind of film where baddies say, “Now you die,” where friends say, “You almost lost your life out there — you have a reason to be concerned,” and where gruff leaders growl, “Let’s do this.” Let’s not.